Mobile devices and other mobile equipment requiring power are used in many settings, including many where spare batteries in sufficient quantities to power the devices and equipment for a given task duration would be an intolerable burden and portable power sources are cumbersome and difficult to carry. One example is Army or Special Force military units operating in terrain where they cannot take a vehicle. A typical mission can last one to two weeks without re-supply. The weight and size of the required batteries for all of the unit's devices (e.g., radios, laser range-finders, computers, night-vision devices, enhanced optical sights, GPS receivers, etc.) for the complete duration of the mission is far more than is feasible to carry. Many other settings require power sources, such as search and rescue missions, geological and geographical survey teams, explorer teams, mountain climbing teams and other setting in which portable power sources are desirable. Portable generators have been available for a long time, but the portable generators and the fuel to operate the portable generators are often too heavy to be hand-carried for long distances.